比较字符串的瓶颈 [英] Bottleneck from comparing strings

问题描述

这是针对 Char * vs String Speed in C ++ 的后续问题。
我已声明以下变量：

This is a follow up question to Char* vs String Speed in C++. I have declared the following variables:

std::vector<std::string> siteNames_;
std::vector<unsigned int> ids_;
std::vector<std::string> names_;

我把这个函数称为数万次，是一个主要的瓶颈。有更有效的方式来比较字符串吗？答案必须是跨平台兼容。

I call this function tens of thousands of times and is a major bottleneck. Is there a more efficient way to compare strings? The answer must be cross-platform compatible.

unsigned int converter::initilizeSiteId(unsigned int siteNumber){
    unsigned int siteId = 0;
    for (unsigned int i = 0; i < ids_.size(); i ++){
        if (siteNames_[siteNumber].compare(names_[i]) == 0){
            siteId = ids_[i];
            break; // Once found, will stop searching and break out of for loop
        }
    }
    if (siteId == 0)
        std::cerr << "Could not find ID for site number " << siteNumber << std::endl;

    return siteId;
}

推荐答案

http://www.cplusplus.com/reference/stl/map/\">map 或无序映射。然后你可以这样做：

Use a map or unordered map instead. Then you can do this:

std::map<string, int>names_;
// ...

unsigned int converter::initilizeSiteId(unsigned int siteNumber){
    unsigned int siteId = 0;
    std::map<string, int>::iterator i = names_.find(siteNames_[siteNumber]);
    if (i != names_.end()){
        siteId = i->second;
    }
    else (siteId == 0)
        std::cerr << "Could not find ID for site number " << siteNumber << std::endl;

    return siteId;
}

这将在O（log n）时间执行，而不是O ）。

This will perform in O(log n) time rather than the O(n) you had before.

如果您有排序列表，还有其他选项，例如二分查找。

There are other options if you have a sorted list, such as binary search.

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